Folded tube for a heat exchanger and method of making same

ABSTRACT

The present invention relates to a multi-port folded tube for a heat exchanger, and, in particular, a multi-port condenser tube and a method of making thereof. The present invention further comprises a folded tube and method of making a multi-port folded tube for a heat exchanger wherein at least one tube locking feature is included.

FIELD OF THE INVENTION

The present invention relates generally to heat exchangers for motorvehicles and, more specifically, to a folded tube and method of makingsame for a heat exchanger, such as an condenser, in a motor vehicle.

DESCRIPTION OF THE RELATED ART

It is known to provide a tube for a heat exchanger such as a condenserin an air conditioning system of a motor vehicle. The tube typicallycarries a first fluid medium in contact with its interior while a secondfluid medium contacts its exterior. Typically, the first fluid medium isa liquid or a two-phase liquid and gas mixture and the second fluidmedium is a gas. Where a temperature difference exists between the firstand second fluid mediums, heat will be transferred between the two viaheat conductive walls of the tube.

In addition, it is known to provide multi-port tubes for condensers inan air conditioning system in a vehicle. Such tubes often have smallhydraulic diameter ports for heat transfer enhancement. In addition, theinterior port walls provide strength to withstand the high-pressurerequirements of the refrigerants in such systems. A known method offorming a tube for a heat exchanger is to extrude the tube in anextrusion process. Particularly with multi-port type exchangers, theextruded tube has become the ‘primary choice’ for motor vehiclecondensers when certain performance levels are required. Extruded tubesof the multi-port type have advantages such as being virtually leak-freeand being a structurally integrated part of the condenser. However,these sort of extruded tubes have the disadvantages of requiringinternal dimensions that must have wide tolerances, in order to keep theextrusion dies life span at a reasonable level to be practical, i.e.tighter tolerances generally reduce die life, whereas the requirement ofwider tolerances of most extruded tubes of this nature means that thereis increased material usage, and, the extruded tubes, therefore, arerelatively expensive to produce.

Yet another known method of forming a tube for a heat exchanger is toprovide a flat, elongated sheet with lugs and the ends of the sheet arefolded to form the tube. The ends of the tube are then brazed. Anexample of such a tube is disclosed in U.S. Pat. No. 5,386,629 issued onFeb. 7, 1995, Ouchi et al. In this patent, the tube may have flow pathsbetween the lugs. However, the quality of the folded tube to headerjoints is related to how small the outside web shoulders can be with thesmaller the better to prevent leakage. U.S. Pat. No. 6,241,012 issued onJun. 5, 2001, Yu et al, disclosed a folded tube and method for makingsuch for a heat exchanger with a base and top and at least an internalweb. The folded tube has very small outside web shoulder radii and aplurality of fluid parts.

U.S. Pat. 6,209,202 issued on Apr. 3, 2001, Rhodes et al, discloses afolded tube and a method of making the same, including a base, anopposing top, and sides interposed between including at least one of thebase and the top having at least one internal web. Compression leads tomultiple parts. Column 3, lines 35-40 and FIG. 4 show an arcuate shapedend feature.

One attempt to overcome the problems of the prior art include designsfor air condition applications wherein one end of tube is ‘locked’ bybinding a number of layers of sheets of material together to lock thetube. By binding, for example, 5 layers of sheet together, to lock thetube end, a very ‘strong’ or ‘solid’ positive lock of the condenser tubeis achieved prior to brazing: however, such a layering and positive lockalso imposes a very rigid relationship between the total tube height,and sheet gauge (tube wall thickness): the total tube height can be morethan about five times wall thickness in some cases.

As described above, attempts to overcome problems in condenser brazingwith flat tubes have often led to solutions that impose very rigidrelationships between total tube height and sheet gauge. However, inthose ‘solutions’ several other problems have been discovered: tubegauge might be not optimized since this rigid relationship provides thatonce tube height is determined, tube gauge is determined also, but notfully due to the structural requirement; this relationship does notallow the use of potential future stronger materials, since reducing thegauge to meet the same structural requirement would not be possible dueto the rigid height gauge relationship; and the reduced flexibility intube design for different applications is less advantageous due to thefact that heat exchanger tube design must consider both heat transferand airside pressure drop.

For exchangers with core depths greater than or equal to 25 millimeters,the higher air pressure drop involved with the increased core depth,would mean it would be optimal to have lesser tube height. On the otherhand, for cores of short depth less than or equal to 22 millimeters,because less airside pressure drop is involved, tube height can beincreased. The present invention overcomes many of the problemsdescribed above.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a multi-port foldedtube for a heat exchanger, and, in particular, a multi-port condensertube and a method of making thereof. It is further object of the presentinvention to provide a folded tube and method of making a multi-portfolded tube for a heat exchanger wherein at least one tube lockingfeature is included.

It is a further object of the present invention to provide a folded tubeformed into multi-port tube wherein tighter tolerance and use ofmaterial occurs due to the tube locking, and, preferably, end-lockingdesign of the present invention. It is a further object of the inventionto provide folded condenser tube with tube end-locking design for use ina motor vehicle, folded from a sheet material to form a multi-port tube.

It is also an object to provide a method to manufacture condenser tubesthat provides for multi-port tubes with advantageous characteristics forautomotive air conditioning applications. It is a further object toprovide folded condenser tubes having very tight dimension tolerances,while at the same time maintaining long life for the ‘roll’ dies.

In addition, it is an object of the present invention to provide for afolded tube that is not an integrated part of the system before brazing,therefore, meeting the performance standards required while avoiding theproblem of perfectly brazing folded tubes.

A further objective is to optimize the folded tube technology byreducing the tube wall thickness and at the same time to avoid the rigidrelationship between total tube height and tube gauge, thus allowingmore flexibility in tube design and optimization of material usage andreduction in cost.

In light of the above, there is a need in the art to provide a foldedtube for a heat exchanger of a motor vehicle that achieves theseobjectives and desires.

SUMMARY OF THE INVENTION

The present invention solves a number of problems often found inextruded technology. Tight dimensional tolerances are achievedconcurrent with achievement of long life spans for the roll dies used inthe process. In its various embodiments, the present invention,therefore, provides cost benefits compared to extruded tubes. Thepresent invention also provides surprising advantages inspite of thefact that in a preferred embodiment a folded tube is generally not anintegrated part of the condenser prior to brazing.

Accordingly, the present invention is a multi-port folded tube for aheat exchanger, and, in particular, a condenser tube, with an improvedtube locking feature. In a preferred embodiment of the presentinvention, a multi-port folded tube is formed from material utilizingthe manufacturing process as described hereinbelow wherein there is atleast one tube locking feature. In preferred embodiments of the presentinvention, the folded tube comprises a tube with the at least one tubelocking feature of the present invention, more preferably, the end tubelocking feature.

The folded tube, and particularly, the multi-port heat exchanger tube,preferably comprises a base; a top spaced from and opposing said base; afirst side interposed between said base and said top along one sidethereof; a second side interposed between said base and said top alonganother side thereof; and each of said base and said top having at leastone internal oriented portion; wherein the at least one top internaloriented portion abuts the at least one base internal oriented portionto define a plurality of fluid ports and wherein there is least one tubelocking feature.

The folded tube in a preferred embodiment of the present inventionincludes a base, a top spaced from and opposing the base, a first sideinterposed between the base and the top along one side thereof, and asecond side interposed between the base and the top along another sidethereof. The folded tube also preferably includes at least one of thebase and the top having at least one internal half web having an initialweb width and an initial outside shoulder radius and capable ofpotentially being compressed when the at least one top half web is ‘faceto face’ or ‘aligned’ with at least one base half web to ‘abut’ or‘contact’ the at least one top internal half web with the at least onebase internal half web and, defining upon closure, a tube with aplurality of fluid ports. The folded tube is then ‘closed’ or lockedwith the end locking feature as described herein below. Therefore, thepresent invention particularly relates to a multi-port folded tube for aheat exchanger, and, in preferred embodiments, a condenser tube whereinthe folded tube of the present invention includes at least one of thebase and the top from a generally planar sheet having at least oneinternal half web essentially aligned face to face and capable ofpotentially abutting when compressed, so that when the at least one topinternal half-web is ‘face to face’ or ‘aligned’ with at least one baseinternal half-web to abut the at least one top internal half web withthe at least one base internal half web, closure provides a tube with aplurality of fluid ports. Also, preferred embodiments of the presentinvention have at least one ‘tube locking’ or ‘closure’ feature the tubelocking or closure feature can be either at the tube end or other thanat the tube end. Preferably, the at least one tube locking or closurefeature is found at tube end.

Also, the present invention is a method of making a multi-port foldedtube for a heat exchanger with at least one tube locking feature. Themethod includes the steps of providing a generally planar sheet, foldingthe sheet, and forming at least one internal half web having,preferentially, a first fold portion and a second fold portion. Themethod also includes the steps of aligning the at least one top internalhalf web and the at least one base internal half web to aide abutting ofthe two half webs. More preferably, the top half web and the base halfweb are face to face or directly aligned so as to provide effectivemulti-port formation. The method further includes the steps of foldingthe sheet and forming a base and a top opposing the base and a firstside interposed between the top and the base and a second sideinterposed between the top and the base such that the at least oneinternal half web abuts or contacts either one of the top or the baseother half internal webs to provide a plurality of fluid ports. The endof the tube is formed by having one sheet end of sheet is bent onto theanother sheet end, and then the both locked ends are bent to form a tubeend.

One advantage of the present invention is that a multi-port folded tubefor a heat exchanger with such a locking feature can be used on with avariety of heat exchangers. In the case such as a condenser is providedfor an air conditioning system of a motor vehicle for condensing liquidrefrigerant. Another advantage of the present invention is that thefolded tube is stamped and folded and is more economical to manufacturethan an extruded tube. Yet another advantage of the present invention isthat the folded tube has half webs that do not extend the entire heightof the ports to be formed, and, therefore, do not require compression tomake a folded top or folded bottom tube portion alone that has to extendto the opposing top or bottom tube portion respectively. Still anotheradvantage of the present invention is that a method of making the foldedtube is provided whereby various tube-end locking features may beutilized. Yet a further advantage of the present invention, particularlyin preferred embodiments, is that it provides a preformed end andsupport versus a ‘traditional’ closed end form that allows seams to beformed and held more closely together, thus eliminating the potential ofmultiple pin-hole sized ‘gaps’ at the end seams of the folded tube.Since the gap is relatively closed, brazing to a header slot, forexample, becomes more efficient and the folded tube more desirable forthese applications.

In preferred embodiments of the present invention, the folded tube maybe an integrated part of the system before brazing or not an integratedpart of the system before brazing. To avoid the problem of perfectlybrazing folded tubes, a preferred embodiment of the present inventiondoes not integrate the folded tube as part of the system prior tobrazing.

Other features and advantages of the present invention will be readilyappreciated, as the same becomes better understood after reading thesubsequent description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a perspective view of a partially closed folded tube;

FIG. 1 b is a perspective view of the closed folded tube with the halfwalls abutting each other;

FIGS. 2 is a perspective view of a closed folded tube with the endfolded;

FIGS. 3 a is a perspective view of a closed folded tube according to thepresent invention, with the end half folded;

FIGS. 3 b is a perspective view of a closed folded tube according to thepresent invention, with the a fully closed end;

FIGS. 4 is a perspective view of a closed folded tube according to thepresent invention, with tube locking feature found other than at thetube end;

FIGS. 5 is a perspective view of another closed folded tube according tothe present invention, with tube locking feature found other than at thetube end;

FIG. 6 is an elevational view of a folded tube, in accordance with thepresent invention, illustrated in operational relationship with a heatexchanger of a motor vehicle;

FIG. 7 is a perspective view of a sheet utilized in a method of makingfolded tubes in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to the drawings and particularly to FIG. 1 a, 1 b and FIG. 2the basic process of tube folding in accordance with the presentinvention, and an embodiment of the subsequent tube 49 of the presentinvention is illustrated. A sheet material 70 is folded progressivelyinto a muli-port 50 tube. The sheet 70 is folded to form severalhalf-webs or internal half webs 40, 44, then bent into tube form. FIG. 1b shows the half web from the top surface 40 and the half webs from thebase surface 44 face-to-face and abutting one another at point 51,together forming webs separating multi-ports.

Referring to FIG. 2, at one end of the sheet ends 34 and 32, are benttwice inwardly on one end 34 yielding three layers and bent once on end32 yielding 2 layers, together forming a 5-layer locked tube end 35,yielding specific relations between tube height and sheet gauge.

Referring to FIGS. 3 a and 3 b, the tube locking features 135,235 areformed. In FIG. 3 a, one end 132 of the sheet is bent onto the other end134 of the sheet 70. Subsequently end 132 and end 134 form locked end135 that are bent to form the tube end 235 of FIG. 3 b. The two lockedsheet ends form another end of the multi-port tube. The end of the tubeis formed by having one sheet end of sheet is bent onto the anothersheet end, and then the both locked ends are bent to form a tube end.

Referring to FIG.4, the tube-locking feature 150 is not at tube end 350.Tube locking feature 150 is found, preferably, at the top of a middleport 351 of the folded tube 350.

FIG. 5 shows another preferred embodiment of the present invention. Thetube-locking feature 250, as in FIG. 4, is not found at tube end.Preferably, the tube-locking feature 250 is found on the inside tubes451 yielding a clearance between the two sheet ends (delta) which doesnot depend on the sheet width.

Referring to the drawings and in particular FIG. 6, one embodiment of aheat exchanger 10, according to the present invention, such as acondenser for an air conditioning system (not shown), is shown for amotor vehicle (not shown). The heat exchanger 10 includes a plurality ofgenerally parallel folded tubes 49, according to the present invention,extending between oppositely disposed headers 14, 16. The heat exchanger10 includes a fluid inlet 18 for conducting cooling fluid into the heatexchanger 10 formed in the header 14 and an outlet 20 for directingcooling fluid out the heat exchanger 10 formed in the header 16. Theheat exchanger 10 also includes a plurality of convoluted or serpentinefins 22 attached to an exterior of each of the tubes 12. The fins 22 aredisposed between each of the tubes 12. The fins 22 conduct heat awayfrom the tubes 12 while providing additional surface area for convectiveheat transfer by air flowing over the heat exchanger 10. It should beappreciated that, except for the folded tube 12, the heat exchanger 10is conventional and known in the art. It should also be appreciated thatthe folded tube 12 could be used for heat exchangers in otherapplications besides motor vehicles.

Referring to FIGS. 7 a, 7 b and 7 c, and FIGS. 1 and 2, a method,according to the present invention, of the making the folded tube 49 isshown. The method includes the steps of providing a generally planarsheet 70 of elongate, deformable material coated with a braze materialforming the base 24 and top 26 having their respective ends 32 and 34edges along a longitudinal length thereof as illustrated in FIG. 7A. Theends 32 and 34 of the base 24 and top 26 can be either flat or arcuateas illustrated in FIGS. 1 a, 2, 3 a and 3 b. Alternatively, for thefolded tube 49, 249, 349 and 449, the ends can be formed as illustratedin FIGS. 3 a through 5. The method includes the step of folding thesheet 70 from the lateral sides to initially form the internal half webs40 on the top with the second internal half web 44 on the base to aninitial predetermined web height and width as illustrated in FIG. 7B.The method also includes the step of aligning the internal half webs 40,44 approximately face to face so that they may abut each other. Themethod includes the step of folding the ends 32 and 34 toward oneanother until they meet to form ports 50 as illustrated in FIGS. 1 b and2. The method includes the step of connecting the ends 32 and 34together. The method includes the step of brazing the folded tube 49 byheating the folded tube 49 to a predetermined temperature to melt thebrazing material to braze the ends 32 and 34 and the internal top halfwebs 40 to the base half webs 44. The folded tube 49 is then cooled tosolidify the molten braze material to secure the ends 32 and 34 togetherand the internal top half webs 40 and the base half webs 44 together. Itshould be appreciated that, instead of the ends 32 and 34, the partition150,250 of the folded tube 349,449 may be formed internally as in FIGS.4 and 5. Accordingly, the folded tube is a cost reduction over currenttubes. The folded tube has internal half webs that are folded andpotentially ‘squeezed’ to maintain a predetermined distance between thetop and base 24. The folded tube also has the internal half webs formingports with a defined hydraulic diameter.

Preferred embodiments of the present invention, as described above, andin particular, as exemplified in FIG. 4, and 5 therefore result in useof less material for tube production, increased refrigerant crosssectional area availability, and, therefore, less internal pressurerestriction for the air conditioning system. In one preferred embodimentof the present invention, the folded tube is a tube having a lockingfeature supported with a ‘T’ shaped wall 150 such that the end edgeswould be in the tube's interior side to maintain an approximately flatwall. In another preferred embodiment, the locking feature is containedwithin a ‘U’ shaped interior wall 451. Preferably, the ‘U’ shapedinterior wall is ‘doubled’ such that the perpendicular end wall portionsor edges would be between the tube's interior walls to maintain closedflat end wall. More preferred would be ‘U’ shaped walls wherein isdoubled In a preferred method of the present invention, referring toFIG. 3 a the planar sheet is shaped such that the width across the tubeformed therefrom is greater than the height of the tube, and the edgesof the planar sheet have a locking feature 135 In the form of a ‘J’.

The present invention has been described in an illustrative manner. Itis to be understood that the terminology which has been used is intendedto be in the nature of words of description rather than of limitation.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, within the scope of theappended claims, the present invention may be practiced other than asspecifically described.

1. A folded tube for a heat exchanger comprising: a base; a top spacedfrom and opposing the base; a first side interposed between the base andthe top along one side thereof; a second side interposed between thebase and the top along another side thereof; and each of the base andthe top having at least one internal half web; wherein the at least onetop internal half web abuts the at least one base internal half web todefine a plurality of fluid ports and wherein there is at least one tubelocking feature.
 2. A folded tube as set forth in claim 1 wherein thegenerally planar sheet is shaped such that in forming the tube the widthacross the tube is larger than the height of the tube.
 3. A folded tubeas set forth in claim 1 wherein the at least one internal half web has aplurality of serrations to mix the fluid flowing through the fluidports.
 4. A method of making a folded tube for a heat exchangercomprising the steps of: providing a generally planar sheet; folding thesheet and forming at least one top internal half web having a first foldportion and a second fold portion and at least one base internal halfweb having a first fold portion and a second fold portion; folding thesheet and forming a base and a top opposing the base and a first sideinterposed between the top and the base and a second side interposedbetween the top and the base such that the at least one top internalhalf web abuts the at least one base internal half web to provide aplurality of fluid ports.
 5. A method as set forth in claim 4 whereinthe step of forming a plurality of internal half webs further comprisesthe step of providing a tube locking feature.
 6. A method of making afolded tube as set forth in claim 5 wherein the generally planar sheetis shaped such that in forming the tube the width across the tube islarger than the height of the tube.
 7. A method as set forth in claim 6wherein edges of the planar sheet formed are flat edges and the tubelocking feature is located on the end of the tube.
 8. A method as setforth in claim 7 wherein the flat edges being formed close on the heightside and have end edges being doubled back against the wall to at leastone material thickness in length.
 9. A folded tube as set forth in claim1 wherein the at least one tube locking feature is supported with a ‘T’shaped wall.
 10. A folded tube as set forth in claim 1 wherein the atleast one tube locking feature is contained within a ‘U’ shaped interiorwall.
 11. A folded tube as set forth in claim 10 wherein the ‘U’ shapedinterior wall is doubled.
 12. A folded tube as set forth in claim 7wherein the tube has folded end edges forming perpendicular walls.
 13. Afolded tube as set forth in claim 11, wherein the tube has folded endedges forming perpendicular walls.
 14. A folded tube for a heatexchanger comprising: a base; a top spaced from and opposing the base; afirst side interposed between the base and the top along one sidethereof; a second side interposed between the base and the top alonganother side thereof; and each of the base and the top having at leastone internal oriented portion; wherein the at least one top internaloriented portion abuts the at least one base internal oriented portionto define a plurality of fluid ports and wherein there is least one tubelocking feature.
 15. A folded tube as set forth in claim 14, wherein atleast one tube locking feature is at the tube end or other than the tubeend.